Saturn moon 'sandblasts' its neighbours white

Particles spewed from Saturn's moon Enceladus are sandblasting neighbouring moons, leaving them sparklingly bright, a new study reveals. If life exists beneath the surface of Enceladus, these particles might be spreading it to other moons, scientists say.

Icy Enceladus is just 513 kilometres wide, but it spews ice particles into space to create Saturn's giant E ring, which is hundreds of thousands of kilometres wide.

During a rare alignment of the Sun, Earth and Saturn in 2005, the Hubble Space Telescope also discovered that Enceladus and some of its neighbouring moons are also extraordinarily reflective.

Now, a new study suggests that high-speed ice particles from Enceladus are "sandblasting" its neighbours to make their surfaces so shiny. The study was led by Anne Verbiscer of the University of Virginia in Charlottesville, US.

Churned-up ice

The researchers found that the moons in the densest part of the E ring - Enceladus and Tethys - are also the most reflective. Mimas, Dione and Rhea, which inhabit more tenuous parts of the E ring, are correspondingly less reflective, but still brighter than moons such as Epimetheus and Janus, which orbit outside the ring altogether.

The team argues that the level of reflectivity depends on how many ring particles slam into the moons. When the icy, micron-sized particles strike the ice-rich surfaces of the moons at speeds of several kilometres per second, they stir up fresh ice that constantly recoats the moons' surfaces.

This keeps them clean and reflective and prevents them from darkening due to the constant bombardment by charged particles from the Sun.

"They churn up the surface and create this fluffy layer," Verbiscer told New Scientist. "Any light hitting them then gets reflected right back."

Lurking life?

The ice particles spewed out by Enceladus are thought to come from subsurface reservoirs of liquid water, leading to speculation that life might lurk inside this moon (see Saturn's watery moon could harbour life ).

If that is the case, then living things may have hitched a ride on ice particles spewed out by Enceladus. This putative life might already have reached other hospitable moons around Saturn, such as Titan, says Joe Burns of Cornell University in Ithaca, New York, US, who was not involved in Verbiscer's study.

"Of course there are questions of whether things would survive the trip, but probably they would," Burns told New Scientist.

Journal reference: Science (vol 315, p 815)

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Saturn's moon Tethys bears the brunt of the particles spewing from its neighbour Enceladus - these particles seem to keep its surface clean and bright (Image: NASA/JPL/Space Science Institute)